The present invention relates to a digital information signal recording/reproducing apparatus for recording a digital information signal (for example, a digital video signal) to a record medium and for reproducing a digital video signal from a record medium and to a method thereof.
A signal processing apparatus used in a digital VTR (Video Tape Recorder) that records/reproduces a video signal (for example, a high resolution video signal) compresses an input video signal so as to decrease the data amount and data rate of a signal to be recorded/reproduced. The compressed video signal is encoded with an error correction code and then recorded to for example a video tape. On the other hand, a signal reproduced from a video tape is decoded with an error correction code, decompressed, and output as a reproduced video signal. As an error correction code, a product code for dually encoding a predetermined number of data words with an inner code and an outer code is used.
When an editing operation is performed with a digital VTR, to check out the edited result, the user normally performs a preview operation. In the conventional digital VTR, to perform the preview operation, an input video signal to be inserted is switched from a signal reproduced from a tape at an edit point. To perform the preview operation, the user checks out the resultant video signal with a monitor.
FIG. 1 is a block diagram showing the structure of a conventional system that performs the preview operation. Referring to FIG. 1, reference numeral 1 is a compression code encoder. Reference numeral 2 is an ECC encoder that encodes the compressed signal with an error correction code. An output signal of the ECC encoder 2 is sent to recording heads through a recording driver and so forth. The recording heads record the signal received from the ECC encoder 2 as diagonal tracks on a magnetic tape. The recording heads are disposed on a rotating drum. In addition, reproducing heads are disposed on the rotating drum. There are two types of reproducing heads that are an advanced reproducing head (ADV head) disposed at an advanced position of a recording head in the rotating direction of the rotating drum and a reproducing head (CNF head) disposed just after the recording head.
With the ADV head, a normal reproducing operation is performed. With the ADV head, a video data recorded on a tape and video data that is input from the outside are synchronized so as to insert a material into data that has been recorded. This operation is referred to as insert editing operation. On the other hand, in the state that recorded data is erased with a full erase head and new data is recorded, with the CNF head, data recorded by a recording head is immediately read so that the user can check out the recorded data.
In FIG. 1, a signal ADV PB RF reproduced by an ADV head is sent to an inner code decoder 3 that corrects an error of the signal with an inner code. An output signal of the inner code decoder 3 is sent to an outer code decoder 5 that corrects an error of the signal with an outer code. The inner code decoder 3 is connected to a RAM 4. Output data of the inner code decoder 3 is written to the RAM 4. The RAM 4 arranges the written data in an outer code sequence. Likewise, the outer code decoder 5 is connected to a RAM 6. Output data of the outer code decoder 5 is written to the RAM 6. The RAM 6 arranges the written data in an inner code sequence. Output data of the inner code decoder 3 is sent to a compression code decoder 7.
Likewise, a signal CNF PB RF reproduced from an CNF head is error-corrected with an inner code by an inner code decoder 9 and a RAM 10. The resultant data is error-corrected with an outer code by an outer code decoder 11 and a RAM 12. The decoders 9 and 11 are connected to the RAMs 10 and 12, respectively. The RAMs 10 and 12 arrange the orders of data. Output data of the decoder 11 is sent to the compression code decoder 7. The compression code decoder 7 selectively decompresses output data of the outer code decoder 5 or output data of the outer code decoder 11 corresponding to the operation mode (recording mode or reproducing mode) of the VTR and outputs a reproduced video signal.
Reproduced signal received through the path of the inner code decoder 3, the outer code decoder 5, and the compressing decoder 7 (PB system) and recorded video data that is received through a path of an EE system are sent to a selector 8. The selector 8 switches video data corresponding to an external control signal. When the insert editing operation is performed and the edited data is previewed, the selector 8 outputs a video signal received through the EE system in a period between an in-point and an out-point. On the other hand, the selector 8 outputs a PB signal in the other period.
FIG. 2 is a timing chart showing an insert editing operation or a preview operation for the edited result performed by the system shown in FIG. 1. FIG. 2 shows the relation of frames of an input video signal and other signals assuming that the input video signal takes place at frame 0. In FIG. 2, a signal for one frame is represented by a rectangle that is nearly the same as the period of one frame. In addition, six equal portions into which one frame is divided represent six segments of compressed data.
A reproduced signal of an ADV head is processed by the inner code decoder 3. The inner code decoder 3 outputs data that has a delay to the output signal of the ADV head by one segment. The outer code decoder 5 corrects an error of the data with an outer code and outputs data that has a delay for a time period of the process thereof. The compression decoder 7 decompresses output data of the outer code decoder 7 and outputs a reproduced video signal that has a delay to the output data of the outer code decoder 5 by one fame. A reproduced video signal is a signal at frame 0. When the reproduced video signal is sent to the selector 8, the reproduced video signal synchronizes with an input video signal received through the EE system. The selector 8 selects an output video signal. A monitoring operation of an output signal of the selector 8 is referred to as preview operation. On the other hand, the operation for switching the reproducing mode to the recording mode and for overwriting the output video signal on a signal that has been recorded on a tape is referred to as insert editing operation.
On the other hand, the input video signal is compressed by the compression code encoder 1. Thus, the compression code encoder 1 outputs a signal that has a delay to the input video signal by one frame. The ECC encoder 2 encodes an output signal of the compression code encoder 1 with a product code and outputs a signal that has a delay to the output signal of the compression code encoder 1 by a time period of the process of the ECC encoder 2. The output signal of the ECC encoder 2 is recorded to a tape by a recording head. The recorded signal is reproduced with a delay of around 0.5 segment by a CNF head.
In the above-described conventional digital VTR, when the preview operation is performed, the following problems take place.
1. In the period between an in-point and an out-point, only a signal that is bypassed (namely, a signal that is received through the EE system) is output. Thus, the user cannot preview a picture that has been compressed. Only a compressed video signal is recorded. The compressing process causes the picture quality of a picture to deteriorate. Although the preview operation is performed to check out the edited result, since the user cannot preview a picture that has not been compressed, the primary objective of the preview operation cannot be satisfactorily attained.
2. While the editing operation is being performed, just before an in-point takes place, the system cannot determine which of the preview operation or the editing operation is being performed. Thus, to allow the system always to handle the preview operation, a signal reproduced by an ADV head should be output until an in-point takes place. Otherwise, since the input video signal does not synchronize with the reproduced video signal, the preview operation cannot be performed. On the other hand, while the editing operation is being performed, to allow the user to preview a picture recorded on a tape, a signal reproduced by a CNF head should be output. However, even if the system is designed to perform the editing operation at an in-point, the system cannot switch a, signal reproduced by the ADV head to a signal reproduced by the CNF head at once. This is because a CNF head reproduces a signal recorded by a recording head. The phase of the reproducing system of the CNF head is completely different from the phase of the reproducing system of the ADV head. If the reproducing system of the ADV head is forcedly switched to the reproducing system of the CNF head regardless of the difference of these phases, a reproduced picture instantaneously disappears due to the phase difference. Thus, while the user is performing the preview operation, he or she cannot perform the editing operation.
3. Regardless of the editing operation, when an input picture is compressed, the user may want to check out the deterioration of the picture quality with the EE system. However, in the above-described structure, since there is no signal path that allows compressed data to be returned to the reproducing system, such necessity cannot be satisfied.
Therefore, an object of the present invention is to provide a digital information signal recording/reproducing apparatus that allows the above-described problems of the conventional digital VTR to be solved and to a method thereof.
A first aspect of the present invention is a digital information signal recording/reproducing apparatus for recording a digital information signal to a record medium and for reproducing a digital information signal from a record medium, comprising a recording signal path having a compression code encoding means for compressing an input digital information signal, and an error correction code encoding means for encoding a compressed signal received from the compression code encoding means with an error correction code, a recording means for recording a signal received through the recording signal path to a record medium, a reproducing means for reproducing a signal from the record medium, a reproducing signal path having an error correcting means for receiving a reproduced signal from the reproducing means and decoding the reproduced signal that has been encoded with the error correction code, and a compression code decoding means for receiving an output signal of the error correcting means and decompressing the received signal, a bypass signal path connected from an output of the compression code encoding means to an input of the compression code encoding means, and a selecting means for selecting a signal received from the reproducing signal path or a signal received from the bypass signal path and for outputting the selected signal.
The error correcting means has an input portion for the reproduced signal, and an input portion for a bypass signal received from the bypass signal path. The bypass signal path is disposed from an output of the error correction code encoding means to an input of the error correcting means.
The error correcting means has a memory for changing the order of signals. The reproduced signal and the bypass signal are assigned different addresses of the memory and written to the respective addresses.
One of the reproduced signal and the bypass signal is selectively read from the memory. The phase of the reproduced signal is matched with the phase of the bypass signal so that the phase difference therebetween becomes 0.
A second aspect of the present invention is a digital information signal recording/reproducing method for recording a digital information signal to a record medium and for reproducing a digital information signal from a record medium, comprising the steps of (a) performing a record signal process for compressing an input digital information signal and encoding the compressed signal with an error correction code, (b) recording a signal processed at step (a) to a record medium, (c) reproducing a signal from the record medium, (d) performing a reproduction signal process for decoding the reproduced signal that has been encoded with the error correction code and decompressing the received signal, (e) bypassing the decompressed signal to a compression code decoding process, and (f) selecting a signal processed at step (d) or a signal that has been bypassed.